Radio beacon system



p 4 F: s. MABRY 2,

RADIO BEACON SYSTEM Filed Nov. 12, 1937 2 Sheets-Sheet 1 WITNESSE$zINVENTOR Farresz 5. Nabry.

I BY W I ATTORN Patented Sept. 17, 1940 STA ES RADIO BEACON SYSTEMPennsylvania Application November 12, 1937, Serial No. 174,205

3 Claims.

This invention relates to radio signalling systems and more particularlyto apparatus for visually receiving radio beacon signals.

One type of radio beacon system in current 5 use comprises a pair ofbeams transmitted from a common source at an angle to each other, theone beam being tone modulated with a code signal such as that whichrepresents the letter A and the other beam being tone modulated with acode signal such as that which represents the letter N. The code letterA is represented by a dot-dash, whereas the code letter N is representedby a dash-dot, these two code signals being so transmitted in timerelationship to each other that the signals will interlock, and whenreceived at such points where the signals are of equal intensity,neither signal will be heard. What the listener will actually hear willbe the tone modulation. The zone or line of equal signal intensity undernormal conditions, should follow the bisector of the angle formed by thetwo modulated beams. If a plane on which a receiver may be mounteddeviates from this line, one or the other of the code signals willpredominate on the receiver, thus indicating the position of the planeto the right or to the left of the radio beacon.

The beacon signals are, according to presentday practice, interruptedevery few minutes to render station announcements and sometimes weatherreports. When receiving the signals over a pair of earphones, one canreadily distinguish the A or the N signals when off course, and noproblem of synchronization occurs since there is no apparatus to besynchronized.

However, when one relies upon some visual indicating means to render thesignals, the operation of the indicator comes to a halt at every stationannouncement or weather report, and it, therefore, becomes necessarythat the indicator be in synchronism with the signals when it againstarts up in operation. Often a pilot will find it essential to switchthe visual indicator out of the circuit in order to listen to some otherconversation or reports, and the same situation arises regardingsynchronizing when the pilot again switches the indicator back into thecircuit.

It is an object of this invention to provide a simple and satisfactorymeans for visually indicating the code signals referred to and enable apilot to determine, by sight, his position relative to the guidingbeacon.

It is another object of this invention to provide a visual indicatorparticularly adapted for the indication of code signals which willpermit a ready and convenient comparison of the intensities of suchsignals.

Another object of this invention is the provision of means for visuallyindicating a plurality of code signals in such manner that the relativeintensities of the signals may easily be compared.

A further object of this invention is to provide an indicator adaptedfor the visual indication of code signals which shall be very sensitivein its response to code signals of low intensity.

A further object of the invention resides in a visual indicator forairplane guiding beacons which shall automatically remain in synchronismwith the beacon signals.

Additional objects of the invention will be brought out in the followingdescription of the same taken in conjunction with the accompanyingdrawings, wherein:

Figure 1 illustrates schematicallya visual indicator embodying thedetails of the invention;

Figs. 2 and 3 disclose in enlarged detail a gear train constructionwhich comprises an important element in the improved indicator;

Fig. 4 is a representation of the signals as transmitted from a beaconstation and illustrates the interruptions occurring for the stationannouncements and the succeeding synchronizing impulse; and,

Fig. 5 illustrates circuit details involved in the feature of theinvention which effects the automatic synchronization of the indicator.

In accordance with the broad idea of the invention, it comprises, whenadapted for the reception of beacon signals, a pair of ionizable gascolumns which are so sensitized, by the application of a positivebiasing potential, that the columns will ionize upon the addition tothebiasing voltage of a signal voltage of very low intensity. Each of thegas columns is so con nected in the circuit, which involves suitablespeed control apparatus and a decoding switch, that the column willrespond to one of the signals only to the exclusion of the other. Thatis, one column will respond exclusively to the code signal representingthe letter N, and the other column will respond exclusively to the codesignal representing the letter A. By supporting these gas columns in aposition adjacent to each other, the relative intensities of the twosignals may be readily determined by a comparison of the height to whichthe column of gas ionizes in each of the columns, the height of the glowproduced by ionization of gas being a function of the signal intensity.

Referring to Fig. 1, for a more detailed disclosure of the improvedvisual indicator, it comprises a pair of gas columns and l, each ofwhich, in actual construction, might comprise glass tubes 2 and 2'filled with an atmosphere of neon gas, these two gas columns beingmounted adjacent each other in a suitable support 3.

The neon gas in these tubes becomes ionizable upon the application ofthe proper value of potential to a pair of electrodes 4 and 4' extendinginwardly for a short distance of the tube at its lower end. Adirect-current biasing potential of a value just sufiicient to bring thegas in these tubes to the point of ionization is applied to theseelectrodes, the electrodes of each tube be ing connected in parallelacross this source of direct-current potential, which might comprise apotentiometer 5 connected across a battery or other convenient source ofpotential, not shown here. One of the connections from the potentiometeris taken from the variable arm, so that the desired potential may beconveniently obtained. Choke coils 9 and 9 segregate the direct currentpotential source from the signal potentials which are fed to theelectrodes 4 and 4.

The code signals are applied to the gas columns from the output of areceiving set, the proper application of these signals to the gascolumns being determined by apparatus so designed as to decode thesignals into the As and Ns, respectively, and to properly apply thesesignals to their respective ionizable columns. Synchronizing means isprovided to assure that the signals will not be distributed aspotentials indiscriminately between the two tubes. For example that theN signals shall not appear across the tube which is intended to displaythe A signals and vice versa.

The apparatus for accomplishing the proper decoding of the signals andthe application thereof to their proper indicating tube comprises adecoding cam or switch 8, the configuration of this cam being such thatin a given direction of rotation, the extended portions of its peripheryrepresent the letter N, whereas the depressed portions represent theletter A, and it will be noted that the two portions of the camrepresenting these two signals bear the same interlocked relationship asthese signals do as transmitted. A contactor 1 bearing against theperiphery of the cam is adapted to be displaced by rotation of the cambetween two fixed contacts 8 and 8', each of which is connected to oneof the electrodes of the ionizable gas columns. The remaining electrodesof these tubes are connected together, and the resulting parallelconnection of these two electrodes is connected to one of the outputterminals ill of the receiver. The other output terminal ill of thereceiver is connected tothe cam controlled contact I through a blockingcondenser H, which excludes any direct current which may be present inthe output circuit.

In order to obtain proper application of the signals to their respectiveindicating tubes, and to assure that the signals as reproduced on theindicator tubes will be in synchronism with the signals as transmitted,the rotational speed of the cam and its initial starting position mustbear the proper relationship to the time period of each signal and theinitial signal transmitted at the moment the indicator is started up inoperation. This is all provided for by the application of a motor l2 thearmature of which is geared to the decoding cam through a speciallyconstructed type of gear train. The motor l2 may be of the shunt type,the speed of which may be brought up to approximately the proper valueby means of a variable resistance l3 connected in series with its shuntfield winding i l. The speed at which this motor is designed to operateis determined by the speed at which the decoding cam should rotate andthe gear ratio of the gear train interposed between the motor and thedecoding cam. When brought up to the proper speed, it will be maintainedat this speed by the tone modulation of the incoming signals applied toasynchronizing field winding IS with which the motor is provided. Thiswinding is connected across the output of the receiver through a seriesfilter comprising a condenser l6 and a choke coil l1, this filter beingdesigned to pass the tone frequency to the exclusion of the code signalsand any other incoming modulations.

The gear train referred to constitutes a very important link in enablingproper synchronous operation of the indicator. Referring to Figs. 2 and3 for a more detailed description of the same, it comprises a drivengear E8, on the shaft of which is mounted the decoding cam, and adriving pinion I9 which is coupled or mounted directly on the armatureshaft of the motor. The driven gear I8 is of decidedly greater thicknessthan that of the pinion l9, the latter being normally held in engagementwith the driven gear at a position substantially flush with one of thefaces of the driven gear by means of a spring 26 on the motor drivingshaft. The larger or driven gear is provided with a cutout ii in itsopposite face and at its periphery, the depth of the cutout beingapproximately half the thickness of the gear. The drivingpinion isadapted to be manually shifted against the action of the spring 23toward the other face of the gear l8 and substantially flush therewith.When so shifted, the pinion will continue to rotate the driven gearuntil the the cutout portion 2! is reached, at which time the pinionwill no longer mesh with the driven gear and the driven gear will cometo a halt.

Under these conditions, the position of the cam 6 on the shaft of thegear l8 should be the same at all times. This particular position of thecam will depend in its initial set-up upon the signal which is firsttransmitted after such station indication or after any otherinterruption in the transmission of the A and N beacon signals.

The actual starting up of the indicator after interruption due tostation announcements, etc., .will be indicated to the pilot by thebeginning of the first code impulse, at which instant the pinion isreleased by the pilot to reengage the driving gear and start operationof the cam. Thus should the code key at the transmitter be so set up asto transmit the letter A immediately after a station announcement, thepilot will wait until he hears the dash and then release the pinion intime to start operation of the cam, which should be so positioned as toapply a voltage corresponding to the dot in the letter A to the properneon tube in synchronism with the dot of the 1etter"A as received, andthereafter as long as signals are broadcast, the indicator will be. insynchronism with the code switch at the transmitter.

In order to make certain that the pilot will receive the startingsignal, namely, the dash of the letter A should he be off course on theN side of the beacon. the transmitter may be so operated as to transmita dash on both sides of the beacon as a signal to indicate to the pilotthe time of release of the pinion for reengagement with the driven gear.The signal in the code form is shown in Fig. 4. In the time intervaldesignated T1, the signal of both channels A and N is shown spaced insuch manner that when the two lines are superimposed, which is the casewhen both signals are received simultaneously, a continuous tonemodulation results. The time interval T2 represents no codetransmission. At the beginning of code transmission after the silentperiod T2, both channels start with a synchronizing signal shown by thedash appearing in both the A and N lines. This signals the pilot torelease the driving pinion l9 formerly described. After thesynchronizing signal, the code appears again in the same sequence asshown in T1.

To relieve the pilot of the necessity of manually synchronizing theapparatus as previously described, there is provided an automaticsynchronizing circuit as disclosed in Fig. 5.

This apparatus consists of a vacuum tube device comprising a triode orany suitable tube 22 coupled to the output of the receiver schematicallyindicated, which feeds the code signals to the input circuit of the tube22 which includes the grid 23 and a voltage source indicated by thebattery 39. The latter is of such magnitude as to bias the grid 23 tocut-ofi point or therebeyond, having its positive terminal connected tothe cathode M. The output circuit between the cathode 3i and the anode El, includes the anode voltage supply indicated by the battery 30 and themagnetizing coil of a relay 25. The latter is of the slow-to-releasetype, its armature making a conductive connection alternately betweentwo sets of contacts 255 and 26' and 21 and 27, respectively, dependingupon the position of the armature of the relay 25. The bridging ofcontacts 21 and 21' by the armature of the relay 25 completes a circuitthrough the battery 28 to the magnetizing winding of a second relay 29,also of the slow-to-release type. This relay actuates a pair of contacts32 and 32'. The former is connected to the contact 26 of the relay 25and the latter to one terminal of the magnetizing winding of anotherrelay 33. The other terminal of this winding connects to the contact 34'actuated by the armature 35 of the relay 33. The corresponding contact34 terminates at the common current source of both relays 25 and 33,namely, the battery 28. The contacts 34 and 34' are normally closed andare opened upon excitation of the relay 33 which in turn opens thecircuit and causes self deenergization. The action thereof will bedescribed when considering the operation of the automatic synchronizingsystem. The armature 35 of the relay 33 is physically so coordinated asto act upon the spring 31 of a clock mechanism 36, whereby thismechanism is wound up to furnish mechanical motive power during the timeintervals of signal transmission, namely, the T1 periods shown in Fig.l. The clock mechanism 36 is intended to replace the driving motor l2shown in Fig. 1. In other words the clock mechanism 35 is intended todrive the distribution cam 5 of Fig. 1. Clock mechanisms of this typeare well known, for example, in the so-called electric clocks in motorcars. These are mechanical clock movements and are periodically andautomatically wound up by an electromagnet. In other words, the spring31 of the clock mechanism. when pulled by the plunger 35 of the relay33, is merely winding up the clock mechanism to thereby store up in thespring suflicient energy to drive an associated gear train, not shown inthe schematic illustration, for such length of time as it takes to sendthe markingsignals A and N. In signal beacons, the duration of time ofthe marking signals T1 of Fig. 4 and the duration of time for thestation identification signals T2 in Fig. 4 which follows each markingsignal period, is maintained constant all the time. Therefore, the clockmechanism is set to run only for such duration of time as it takes tosend the marking signal. At the end of this time it stops, whereby thecam 5 connected to the clock mechanism will stopalso. During the stationidentification period T2 when no beam signals are sent, the clockmechanism remains deenergized and is wound up again when the firstsignal impulse following T2 is received. This will be more fullyexplained in the following description of the operation of the circuit.

In the operation of the circuit thus far described, and during theperiods of no-signal reception, T2 in Fig. 4, the armature of the firstslow-to-release relay 25 will be deenergized and contact the lowercontacts 2'! and 2'5, thus maintaining the circuit through the secondslow-torelease relay 29 in closed condition. Consequently, the armatureof this second relay will occupy its in position and will bridge thecontacts. 32 and 32', thereby setting up a circuit from 26 through 32and 32, solenoid 33 and contacts 3% and 3A to battery 28. Now When thefirst signal impulse following T2 is received, it overcomes the blockingbias of battery 39 on grid 23, allowing current from battery 30 toenergize relay 25. When the latter closes contacts 26 and 26, thesolenoid 33 becomes energized, thereby winding the spring 37. As statedbefore, spring 37, when Wound, will drive cam 6 of Fig. 1 just so manyrevolutions corresponding to the period between T2 periods which areregular and unchanging in number at all times. After the T2 period,relay 25 remains energized until the next T2 period and likewise therelay 29 remains deenergized. Therefore, as a result, the first impulseexcites the solenoid and draws in its plunger and winds up the spring.The movement of the plunger, however, breaks the circuit to the solenoidat the normally closed contacts 34 and 3 3 to permit the plunger toreturn to its initial position. By this time, the circuit to thesolenoid 33 will have been broken at the contact associated with thesecond relay 29.

It is to be noted in the operation of this circuit that the firstimpulse transmitted after the station announcement period results in asudden winding of the spring followed by its return to its normalcondition.

This sudden winding and release of the spring occurs only on the firstimpulse and not thereafter during the period of transmission of codesignals since the first relay remains energized throughout thesignalling period due first of all to the fact that the signals are ofinterlocking character and the tone modulation will, therefore, remainpractically continuous, and secondly, due to the fact that this relay isof the slow-torelease type and should any breaks occur in the signal fora short duration, the relay will carry over through these periods.

The action of the spring 31 is utilized as stated before in supplyingenergy to a clock motor or other driving means suflicient to drive thedeiing cam and continue the rotation thereof iy throughout a period ofcode signal transssion. ['he tone modulation referred to previously isthe order of 1000 cycles per second. To preit atmospheric disturbancesfrom interfering ;h the operation of the first relay during the 1e whenstation announcements are being .de, there is inserted a filter betweenthe outa of the receiver and the amplifier to be con- :ted thereto, thisfilter being designed to pass zrgy at the tone frequency and to excludeen- :y at other frequencies, thus assuring operan of the first relay inresponse to the tone dulations only. In the initial adjustment of theindicator, the :oding cam is so positioned on the shaft of a driven gearthat the effect on one or the ler of the ionizable gas columns willcorremd toand be in synchronism with a portion the signal which istransmitted after the first initial starting impulse, which, asexplained We, may be the dash corresponding to the ;er T. When soadjusted, the apparatus is and ready for operation. teferring to theoperation of the indicator, en no automatic synchronizing means as )Wllin Fig. 5 are employed the cam driving tor i2 is brought up to properspeed, and its led is held constant by the tone modulations ng fed tothe synchronizing winding I5 ough the tuned circuit I0 and I! in serieswith s winding. At the same time impulses corrending to the code signalsare fed from the outof the receiver to the neon indicating tubes way ofthe decoding switch, the action of ich is under the control of thedecoding cam. [en the apparatus is properly adjusted, and uming theletter A is to be indicated on the ;-hand neon tube, the decoding camwill opte to close the circuit to the A tube through decoding switchduring such time periods as dash and the dot of the signal A are beingeived by the receiver; and conversely the deing cam will close thecircuit to the N tube ing such time periods as the dot and the dash thesignal N are being received by the re- 761. With the motor held at theproper speed, reproduction of the code signals at the proper e and intheir respective tubes will continue long as there is a continuousbroadcasting of code signals without interruption either at transmitterdue to station announcements, or due to interruption by the pilot shoulddesire to listen in on his receiver to announceats or broadcasts on adifierent wave length. )nce the apparatus gets out of synchronism to anyof the above reasons, the pilot merely hes the pinion from its normalposition so t it will mesh with the cutout portion of the ven gear andhalt rotation of the same with decoding cam in a predetermined position.in knowing that the apparatus will again be synchronism if started up onthe dash of the er T, he may start the apparatus up again merelyreleasing the pinion and permitting 0 return to its normal position inengagement h the driven gear at the moment that he re the dash of theletter T in his earphones. be single dash of the letter T is sentsimultaneously by both signal beams and is for the purpose of providingan impulse for marking the proper time when the rotation of the cam 6may be started either by the pilot or automatically as previouslydescribed. If the interruption to the operation of the indicator is dueto a station announcement, the pilot will merely listen for the firstimpulse after the station announcement, this impulse, of course,corresponding to the dash of the letter "1".

Where the automatic synchronizing feature is embodied in the indicator,the pilot is relieved of the burden of placing the apparatus insynchronism, as this result will automatically be obtained after eachinterruption due to station announcement, etc.

While the invention has been disclosed in great detail, various changesand modifications may suggest themselves to those skilled in the art,and it is not intended to be limited to the specific embodimentdescribed except as may be necessitated by the prior art and theappended claims.

I claim as my invention:

, l. A visual indicator for the reception of a pair of intersectingradio beams having identical carrier frequency, each being identified bymodulation of dot and dash characters, said modulation beingperiodically interrupted by signals of a different character, comprisinga pair of gaseous columns each representing one of said beams and eachadapted upon energization to become luminous to a height depending uponthe intensity and modulation character of said beams respectively, andmeans for establishing a uniform order of sequence between luminousexcitation of said columns with respect to said beams after each saidperiodic interruption.

2. In a system for visually interpreting aural signals transmitted overa carrier wave modulated in sequence alternately by two sets ofpredetermined code characters, means for impressing said characters insequential order discriminatingly as to said sets upon an indicatingdevice, said means including a rotatable cam coupled toa driving motorby means of a gear train, said cam having peripheral configurations,switching means actuated by said cam for alternately energizing saiddevice, the speed of rotation and the peripheral configuration of saidcam cooperating with said switching means in such manner as to segregatesaid setsof characters into groups of like signals whereby saidindicating device becomes discriminatingly energized in sequence by likesets of said code characters.

3. In a radio beacon system of the type wherein a guiding beacon isestablished by the transmission of a pair of radio beams at an angle toeach other, said beams being of identical carrier frequency anddifferentiated by successive transmission of modulation charactersinterlocking to form an uninterrupted tone modulation, visual means forindicating the reception of said beams comprising a pair of ionizablegas columns each representing one of said beams, and means for causinguniform ionization of both of said columns in accordance with said tonemodulation and for causing differential ionization of said columns inaccordance with modulation characters of ether of said beams.

FORREST S. MABRY.

